Photosynthesis and photoprotection dynamics in cultured dinoflagellate Lingulaulax polyedra (formerly Lingulodinium polyedra)

The study of photosynthesis and the growth of phytoplankton organisms is important for a better understanding of primary productivity, especially in precursors of harmful algal blooms (HABs), such as the dinoflagellate Lingulaulax polyedra (formerly Lingulodinium polyedra). The effect of nutrient availability (low concentration: 200.3/10.3 μM, medium: 280.5/14.8 μM, and high: 479.7/26.3 μM NaNO₃/NaH₂PO₄) and irradiance (50, 150, 300, and 750 μmol quanta m^-2 s^-1) on the growth rate (μ), photosynthetic efficiency (α), relative electron transport rate (rETR), pigment concentration and absorption coefficient in in vitro cultures of L. polyedra was analyzed. It was observed that μ did not vary with nutrient concentration or irradiance (p > 0.05, AN), and the stationary growth phase was observed in all treatments on day 9 of cultivation. As irradiance increased, significant increase in photoprotective carotenoid pigments and a reduction in photosynthetic pigments were observed among treatments. L. polyedra showed the highest α during the stationary phase in treatments under 50 μmol quanta m^-2 s^-1 irradiance, with a value of 0.259 ± 0.005. Cultures did not show differences between nutrients, suggesting that the species-specific response to light availability depends on the growth phase. This study suggests L. polyedra adjusts its energy use based on irradiance, prioritizing growth in the exponential phase and optimizing photosynthesis for nutrient distribution in the stationary phase. This study contributes to understanding the species' resilience at different irradiances and nutrient concentrations, which can help to understand the adaptations that allow it to potentially form harmful algal blooms (HABs).